DNA the Key to Fish's Tale of Survival

AUSTRALIA - Researchers have played the role of matchmaker to help bring two freshwater fish species back from the brink of extinction.

Flinders University scientists in South Australia have pioneered the use of untapped DNA information to improve the success of captive breeding and reintroduction programs for the native pygmy perch.

Researcher Catherine Attard said the implementation of the full potential of DNA methods could be used to maintain diversity in captive breeding programs to give a wide range of threatened species a better chance of survival when released back into the wild.

“That’s rarely done and could be very useful in other areas in captive breeding especially with the big biodiversity crisis that we are having at the moment where many species are becoming extinct around the world because of human impacts,” she said.

“This DNA technique can be used in parrots or mammals or any other species so that’s the really awesome thing about it.”

There have been local extinctions of native fish in the Murray River, Australia’s biggest river, since European settlement in 1788.

The two species - the Yarra pygmy perch (Nannoperca obscura) and southern pygmy perch (N. australis) - became extinct in the lower Murray-Darling Basin when their habitat dried out in 2008 during Australia’s decade-long millennium drought.

Fortunately, samples of the pygmy perch had previously been rescued and kept in captivity.

Dr Attard said the likelihood of inbreeding among threatened species increased as their numbers dwindled in the wild, potentially reducing their genetic diversity.

Dr Attard said the key to the Flinders University program’s success was the use of DNA to maintain genetic diversity in captive breeding programs.

“By using DNA we can actually tell which ones are more likely to be related to each other and make sure in captivity at the very start of the program that you don’t breed those individuals together,” she said.

“We examined the DNA of the rescued Yarra pygmy perch and found that human impacts had not yet reduced their genetic diversity, which is great news.

“DNA is inherited between generations making it possible for us to design crosses between unrelated individuals to preserve the genetic diversity of the population.”

However, it was a different story with the rescued southern pygmy perch.

“In their DNA we found signs of a decrease in their genetic diversity, and that the decrease started at the time of European settlement,” Dr Attard said.

“Southern pygmy perch may struggle to persist in the lower Murray-Darling Basin due to their unnaturally low genetic diversity. If their numbers do not increase, we may need to consider supplementing their genetic diversity with that from other populations, which are nowadays mostly restricted to the upper reaches of the Basin.”

Historical records indicate that the southern pygmy perch population contracted in distribution due to European settlement, but that the Yarra pygmy perch population always had a narrow distribution. This explains the different genetic patterns of the species.

Flinders Australian Research Council Research Fellow Professor Luciano Beheregaray led the successful implementation of the full potential of DNA to save the two species.

Professor Beheregaray said the breakthrough strengthened the “last line of defence” against species and population extinction during a time of growing human-caused loss of biodiversity.

“Captive breeding programs aim to preserve the genetic diversity held in the target population,” he said.

“This is because the genetic diversity has developed through evolution and so defines that population.

“It allows the individuals to survive and reproduce in their natural habitat and adapt to environmental changes.”

The Flinders research team conducted a genetic-based breeding program and produced more than 1000 offspring for each species. The offspring were released into the lower Murray-Darling Basin from 2011 onwards when the drought ended and some of their aquatic habitats were restored.

Monitoring of the reintroduced populations has shown that the pygmy perch are not only surviving but are also reproducing in the wild.

“It will still be some time before we know if their wild populations are self-sustaining, but the recapture of captive-born individuals in the wild after three years since their release is fantastic news,” Professor Beheregaray said.

The researchers emphasise that it is paramount to understand how natural genetic diversity has been influenced by humans and historical natural processes to better inform captive breeding and reintroduction programs of any endangered species.

The findings have been published in the leading journal Conservation Biology.